What is the best time to trim bushes?

That will depend on the type of bushes.

Irene, ask at a local nursery or, better yet, do an internet search on the type of bush. An internet search will give you a chance to compare answers for your type of shrub. Pruning is completely based on the type of plant and also on your reason for pruning, such as control growth, plant renewal, or to reduce the size of the plant. Also, sometimes your local extension service can be of help.

If it is a flowering shrub, trim after blooms fade. All other shrubs can be trimmed anytime.

Depends on the bush so look it up or ask a neighbor who has the identical plant and whose a successful gardener. Some bushes, like roses, get pruned in early spring and some after the bush is done blooming. Every county has a Cooperative Extension Office under the name of your county; call them and they can answer many garden questions. I once trimmed a clematis vine at the wrong time and it died, so do some research before cutting things back. It is good to save the label the plant came with but the label does not always tell you everything about plant care but at least you will have the name. Check out used books stores and on-line used book dealers and buy some garden reference books because they will be helpful regarding many aspects of gardening.

If they are flowering bushes a good rule of thumb is if it blooms in the spring you trim it and cut it back in the fall. If it blooms in the summer you trim it and cut it back in spring.

As my husband's grandfather use to say, "Trim anytime you have the time and energy".

Depends on the bush. Some bloom on old wood, some on new. Mess up and you won't get blossoms. Best to know what they are and look them up or check with your nursery.